The present invention relates, in general, to transitions which are employed to interface dielectric waveguides to coplanar metallic microwave transmission lines.
In recent years, there has been increasing interest in designing integrated electronic circuits for operation in millimeter wave frequency ranges on the order of 100 GHz. At such frequencies, transmission lines used for component interconnection can attenuate the signal significantly due to the fact that the metallized regions of the transmission lines are imperfect conductors and cause resistive power dissipation. Dielectric waveguides can provide a much lower-loss guiding structure for signal propagation at these frequencies, and consequently are an attractive solution to the problem of signal power loss. In addition, dielectric waveguides can be manufactured to have greater mechanical flexibility and can therefore be used in a variety of applications in which geometrical constraints and signal attenuation prohibit the use of transmission lines. For example, signals can be routed throughout computers with less attenuation if dielectric waveguides are used in place of transmission lines. In addition, the mechanical flexibility in these guides makes them simpler to use than either transmission lines or conventional metallic waveguides for the interconnection of computers or of computer components.
These low-loss dielectric guiding structures, however, still require electrical connection to active high frequency structures, such as semiconductor devices. Thus, in order to use dielectric waveguides for component interconnection, it is necessary to combine both types of signal guiding technologies in high frequency integrated circuits. Since most high frequency integrated circuits employ coplanar metallic transmission lines for interconnection of devices, the problem must therefore be solved of interfacing signal propagation in coplanar metallic transmission lines to signal propagation in dielectric waveguides. If this can be accomplished successfully, the dielectric guide may be used for longer range signal interconnect requirements in the integrated structures, and the coplanar transmission line sections can be used for local signal propagation as needed for component requirements. In addition, the dielectric guiding structure lends itself to integration with optical components, thus coplanar metallic transmission line to dielectric waveguide transitions can also serve to combine microwave circuits and optical components in high frequency optical electronic integrated circuits.